Abstract
The flow interaction between bubbles is known to have an influence on acceleration of the bubbles rising velocity and the bubbles shape under static pressure field. We previously reported that pressure oscillation is effective for enhancing rising velocity of a small bubble in viscous shear-thinning fluid. In the present study, flow interaction between two small bubbles placed in the vertical direction under pressure-oscillating field, which is applied from the bottom side, is investigated experimentally. The three fluid types of different rheological properties, sodium polyacrylate, carboxy-methyl cellulose sodium salt and xanthan gum, are selected and tested. With a help of strobe scope lighting, we successfully monitor trace of the moving bubbles clearly through a high density video camera. Two non-dimensional parameters of each of the bubbles, normal rising velocity of bubble ε and non-dimensional acceleration Gb, are compared for the test fluids. It was found that the rising velocity of the lower bubble is higher than that of the upper bubble; that is strongly enhanced in the case of closer bubbles; and finally the bubbles move together and form a cluster, whereas natural rising velocity of the bubbles without pressure oscillation are the same. In addition, a ratio of distance between the bubbles center L and bubble diameter D and non-dimensional rising velocity ε are compared. After experiment we found that rising velocity of the lower bubble depends on the distance between bubbles and non-dimensional acceleration.
